1. Field of the Invention
The present invention relates recording and/or reproducing apparatus, recorders, pulse-code modulated (PCM) audio signal recorders and so forth. more specifically, the invention relates to an automatic tracking system for a magnetic recording and/or reproducing apparatus, which can satisfactorily control tape feed speed for fine tracking.
2. Description of the Background Art
In modern video tape recorders, automatic tracking systems provide automatic adjustment of tracking volume without requiring manual operation. In a typical automatic tracking system, the speed of a capstan motor is so controlled that a control signal recorded in a control track on a magnetic tape can be maintained in a predetermined phase relationship to a rotary drum. By way of this, the scanning start timing of a magnetic head is controlled to the same timing as a recording to assure reproduction of a well adjusted video image.
The ideal reproduced control signal has a symmetric waveform with respect to a center and peak signal level. Using such an ideally reproduced control signal, the automatic tracking control can be done very efficiently by adjusting the capstan motor speed to obtain the peak level of the control signal, by adjusting the phase relationship between the magnetic head and the control track to obtain the peak level of the control signal, optimal video image reproduction can be achieved.
However, it is not possible to obtain an ideally reproduced control signal due to the tolerances involved in the installation of tape drive systems and rotary heads, which tolerances necessarily cause slight fluctuation of the angle of a scanning trace of the magnetic head, or meandering of the scanning trace. Such tolerance in the scanning trace of the magnetic head versus the magnetic tape will cause distortion of the reproduced control signal. A distorted control signal makes it difficult to detect the optimal phase relationship between the magnetic head and the recording tracks on the magnetic tape.
In a typical case, a practically reproduced control signal has an asymmetric waveform with respect to the peak level of the control signal or has a multi-peak waveform. when a multi-peak waveform control signal is reproduced, a conventional automatic tracking system selects one of the peaks for adjusting the phase relationship between the magnetic head and the tape track. In contrast to this, it has been noted that, through manual adjustment by means of a manually operable tracking volume, improved fine reproduction of the video image can be obtained at a phase relationship intermediate between the points where the peak level of the control signal is obtained. Therefore, conventional automatic tracking systems fail to provide optimal tracking adjustment. Additionally, in a case where an asymmetric waveform control signal is produced, a conventional automatic tracking control system adjusts the phase relationship between the magnetic head and the tape track at a point where the maximum level of the control signal is obtained though such point is offset from the center point where the optimal video image reproduction performance can be obtained. In such case, jitter causes the phase relationship to shift and the reproduced signal level tends to drop rapidly, causing a substantial degradation of the reproduced video image.